1. Field of the Invention
The present invention relates to a fuel cell which generates electrical power by use of an electrochemical reaction. The present invention further relates to a membrane electrode assembly, a catalyst layer for gas diffusion electrode and a method for manufacturing the same, preferably applied to a fuel cell or the like.
2. Description of Related Art
A fuel cell is a generator having a structure including a pair of electrodes between which an electrolyte is interposed, one electrode being supplied with fuel and the other electrode being supplied with oxidant, thereby converting chemical energy into electric energy with high efficiency. The fuel cells are classified into, for example, a polymer electrolyte fuel cell, a phosphoric acid fuel cell, a molten carbonate fuel cell, and a solid oxide fuel cell, depending on the type of the electrolyte. Among them, attention has been drawn to the polymer electrolyte fuel cell in terms of the high energy conversion efficiency and the reduction in size, and the polymer electrolyte fuel cell is expected to be applied to, for example, fuel cell vehicles, stationary cogeneration systems, portable power supplies, power supplies for information devices.
The polymer electrolyte fuel cell is classified into a cation exchange type and an anion exchange type depending on the electrolyte. When the cation exchange type electrolyte is used, the environment in the electrodes is acidified. When the anion exchange type electrolyte is used, the environment in the electrodes is alkalified. While being varied depending on the classification of the electrolyte or the feed fuel, a catalyst layer typically contains a metallic catalyst such as platinum or platinum alloy, a carbon powder that supports the metallic catalyst, and an ion conductor.
It is indispensable to improve the performance of the catalyst layer arranged in electrodes (anode and cathode) in order to improve the characteristics of the polymer electrolyte fuel cell. Accordingly, catalyst layers have been energetically researched and developed, and a number of proposals have been made.
Yangchauan Xing, “The Journal of Physical Chemistry B”, 2004, 108, p. 19255-19259 proposes an electrode catalyst that uses carbon materials such as carbon nanotubes to support a metallic catalyst in order to improve catalytic activities of an oxidation reaction of hydrogen in the anode and a reduction reaction of oxygen in the cathode. H. Yano et al. “Phys. Chem. Chem. Phys.”, 2010, 12, p. 3806-3814 reports that durability is improved by graphitization due to a heat treatment of carbon which is a support body, and the size control of platinum nanoparticles. International Patent Publication No. WO 2011/096230 discloses a technique of using nanoparticles forming a network-like structure and having a hollow inside for a medical agent.